A fused heterocyclic compound and a salt thereof, which have an excellent JAK3 inhibitory activity, and are thus useful as an agent for treating and/or preventing diseases caused by undesirable cytokine signal transduction (for example, rejection during live-donor transplantation, rheumatism, psoriasis, autoimmune diseases, asthma, atopic dermatitis, Alzheimer's disease, and atherosclerotic disease, etc.), or diseases caused by abnormal cytokine signal transduction (for example, cancer and leukemia, etc.), are described in Patent Document 1. Among these, 4-{[(1R,2s,3S,5s,7s)-5-hydroxy-2-adamantyl]amino}-1H-pyrrolo[2,3-b]pyridine-5-carboxamide represented by the following formula (I), as disclosed in Example compound Ex. 121, is a compound which exhibits an excellent activity and is expected to act particularly as an agent for inhibiting rejection reaction during organ/tissue transplantation or for treating rheumatism, psoriasis, or the like.

The solid stability of a compound to be a development candidate of a pharmaceutical is an important factor in industrial operations as well as maintenance of quality. For the stability of a drug substance itself, it is necessary to evaluate the stability of quality required to maintain the efficacy and the safety of pharmaceutical products, and to obtain information required to determine the storage methods and the shelf life for pharmaceutical products. Therefore, a stability test is considered as one of the most important tests for the preparation of pharmaceutical products (Thermal Measurement, 2004, 31(2), pp. 80-86).
In Patent Document 1, a free form of the compound of the formula (I) is disclosed, but a crystal of the compound is not disclosed. There is a demand for a bulk material for the preparation of a pharmaceutical product, which is suitable for formulation and is physicochemically stable in terms of quality assurance.